This invention relates to a new process of forming cis- or trans-thiazine-indigo compounds in aqueous media. This invention also relates to a process of converting the cis-thiazine-indigo compounds into the trans-thiazine-indigo isomers, which are known to be pigments.
Thiazine-indigo compounds are an important series of pigments. Prior art processes for forming these pigments involve the reaction of certain o-aminomercapto-carbocyclic or -heterocyclic compounds with maleic acid or a derivative thereof in the presence of a solvent. Solvents useful for this purpose were either a carboxylic acid (which also acted to catalyze the reaction) or an inert polar aprotic solvent.
Thus, in DE 2151723 a process is described for making certain symmetrically substituted benzothiazine-indigo compounds wherein certain substituted ortho-aminomercapto-carbocyclic or heterocyclic compounds are reacted with a maleic acid derivative in a carboxylic acid, e. g. acetic acid. By symmetrically substituted is meant that there is identical substitution on each of the thiazine rings.
In DE-OS 2536120 a process is described for making certain other symmetrically substituted benzothiazine-indigo compounds wherein certain substituted ortho-aminothiophenols are reacted with a maleic acid derivative in an inert polar aprotic solvent. It is alleged that the benzothiazine-indigo compounds so formed, display improved pigmentary properties, e. g. brighter and cleaner shade over the compounds made in a carboxylic acid solution, however, they can only be produced in poor yield.
There still remains a need to provide a further improved process of forming thiazine-indigo compounds, especially tans-thiazine-indigo pigments.
Accordingly, the invention provides in one of its aspects an environmentally friendly water-based process of forming thiazine-indigo compounds according to the formula (I) [cis-isomers]and (II) [trans-isomers]
wherein
R1 and R2 independently represent the atoms necessary to complete the formation of a substituted or unsubstituted aromatic or aliphatic carbocyclic or heterocyclic ring system, and
R3 is hydrogen, C1-12alkyl or phenyl,
comprising the step of reacting in the presence of an aqueous system compounds of formula (IIIa) and (IIIb) 
wherein
R4 and Rxe2x80x24 independently are H or a metallic ion selected from Na+, K+or Zn2+
with a compound of formula m [trans-isomers] or (V) [cis-isomers]
wherein
Hal is Cl or Br,
both R5 independently are a leaving group commonly used in substitution reactions at carbonyl carbon atoms, e. g. Cl or C1-5-alkoxy or OH.
The aqueous system comprises water or water and an acidic catalyst or water and a basic catalyst or a mixture of water and a water miscible solvent, like alcohols.
Particularly interesting is the possibility to use dihalomaleic acids or dihalomaleic acids, already prepared or generated in situ.
It has been discovered that fumaric derivatives of formula (IV) give the trans-isomer of formula (II) and the maleic derivatives of formula (V) give the cis-isomer of formula (I).
Preferably the molar ratio of the reactants is 1:1:1.
The process is carried out in the presence of a carboxylic acid or of a salt thereof, e. g. acetic acid, or an inorganic acid or salt thereof, e. g. sulphuric acid or hydrochloric acid or phosphoric acid, which also acts as a catalyst, and an aqueous medium, e. g. water or a mixture of water and a miscible solvent, preferably an alcohol with 1-5 C-atoms, e. g. ethanol, methanol or butanol.
The basic catalyst is an inorganic base, especially sodium or potassium hydroxide or an organic base such as triethylamine.
The reaction is preferably carried out in water in the presence of 0 to 95% by weight, preferably 10% by weight of an acid catalyst, e. g. acetic acid or hydrochloric acid or sulphuric acid or phosphoric acid.
The reaction temperature is preferably of the order of 0 to 150xc2x0 C., more preferably between 10 and 100xc2x0C.
Compounds of formulae (IIIa), (IIIb), (IV) and (V) are known compounds or can be prepared in analogy to known methods.
The thiazine-indigo compounds of formulae (I) and (II) may be symmetrically substituted, that is R1 and R2 are identical. Alternatively, they may be asymmetrically substituted, that is, R1 and R2 are not identical. Non-identity refers to either the ring systems R1 and R2 being different or, in the event that the ring systems are identical, the substituents attached to the respective ring systems are different.
Preferred thiazine-indigo compounds formed according to the invention are those asymmetric compounds wherein R1 and R2 are independently selected from the group consisting of 
In a more preferred process according to the invention, R1 consists of the atoms necessary to complete a benzene ring which is optionally substituted with, for example halogen or alkyl and R2 consists of the atoms necessary to complete a ring system which is a symmetrically substituted benzene ring or a different ring system, e. g. naphthalene, pyridine or 1,4-benzodiazine.
The thiazine-indigo pigments formed according to the invention may be substituted on the ring systems with one or more of any of the non-water-solubilising substituents common in the art of pigments. Preferably the ring system substituents are selected from the group consisting of halogen, trifluoromethyl, nitro, cyano, alkyl, alkoxy, amino, alkylamino, thioalkyl, phenoxy, phenylamino, phenylthio, acyl, acyloxy or acylamino.
The term xe2x80x9chalogenxe2x80x9d includes fluorine and especially chlorine and bromine. The term xe2x80x9calkylxe2x80x9d or xe2x80x9calkoxyxe2x80x9d comprises preferably radicals with 1 to 4 carbon atoms. The terms xe2x80x9calkylaminoxe2x80x9d and xe2x80x9cphenylaminoxe2x80x9d include for example N,N-dialkylamino and N,N-diphenylamino as well as N-monoalkyamino and N-monophenylamino.
The aforementioned alkyl, alkoxy, phenyl and phenoxy substituents may themselves contain one or more substituents selected from the substituents hereinabove described.
A further aspect of the invention relates to the cis-isomers of formula I which are new compounds except of the compound of example 1 in which R1 and R2 are benzene rings.
Another aspect of the invention is the process of converting the cis-isomer of formula (I) into the trans-isomer of formula (II), by thermal treatment in an inert polar solvent, in the presence or not of an acidic catalyst, that can be a carboxylic acid, e. g. acetic acid, trifluoromethane sulfonic acid or para-toluene sulfonic acid or another acid usually used in organic chemistry.
The inert polar solvent can be chlorobenzene, nitrobenzene, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, or a high boiling point alcohol, like ethylene glycol, dipropylene glycol methyl ether.
The thermal treatment comprises temperatures of from 100 to 250xc2x0 C., preferably of from 100 to 180xc2x0 C., more preferably of from 130 to 160xc2x0 C.
The trans-thiazine-indigo pigments formed by the conversion process according to the invention are suitable for the mass pigmentation of suitable substrates including synthetic polymers, synthetic resins and regenerated fibers optionally in the presence of solvents. These substrates more particularly include oil, water and solvent based surface coatings, polyester spinning melts, polyethylene, polystyrene and polyvinyl chloride molding materials, rubber and synthetic leather. Furthermore, the pigments can be used in the manufacture of printing inks, for the mass coloration of paper and for coating and printing textiles.
Based on the substrate to be mass pigmented the thioazine-indigo pigments according to the invention are used in amounts of 0.01 to 30% by weight, preferably 0.1 to 10% by weight
When applied to the afore-mentioned substrates the thiazine-indigo pigments are found to be resistant to migration and fast to light, and show fastness to washing, chlorite, hypochlorite and peroxide bleaching, rubbing, overspraying and solvents. Notably, the pigments display high tinctorial power, good transparency and good heat stability.
The invention is further illustrated by means of the following examples in which all percentages and all quantities are expressed by weight.